Most industrial bakeries use tunnel ovens, traveling tray ovens, or other conveyorized ovens, all either direct or indirect heated for baking dough into bread. The conveying devices in all of these open ended ovens for advancing the bread products through the oven usually are some type of heavy duty continuous roller chain or mesh belting. These chains carry the pans or other carriers that support the baker's dough through the high temperature of the oven that bakes the dough. Ovens may have two or three parallel roller chains, or mesh belting, used for moving pans that carry the work products through the ovens. The oven conveyor chains are exposed to extremes of temperature from room temperature to in excess of 600° F. The ovens may have from a few hundred feet of chain length to more than a thousand feet of chain length that transport the pans that carry the work products through the oven.
Oven chains typically are roller chains that resemble a bicycle chain, in that the oven chains include a series of chain links that each includes a pair of parallel elongated side plates held to each other at their opposite ends by axles, with rollers mounted on the axles. The teeth of driving sprockets fit into the spaces defined by the rollers and the side plates, and the rotation of the sprockets drive and guide the chain links, causing the chain to move along its length. The teeth of the sprockets apply forces to the chain links and the chain links deteriorate over time.
Examples of some prior art oven chains are illustrated and described in U.S. Pat. Nos. 4,294,345; 5,147,033; and 7,086,525.
Oven chains usually have a life of five to ten years. In order to maintain the life of oven chains, the oven chains must be lubricated frequently, sometimes several times per day, usually with expensive high temperature resistant lubricant.
Oven roller chains are very large, heavy and expensive. Pans, trays, plates, mesh belts and grids, herein after referred to as “pans”, are each mounted to a link of the chain and add to the cost and weight of the chain. When the large and heavy oven chains begin to wear out, the maintenance people cannot expect to just replace a single worn link in a chain since it is likely that several links have become worn and the pitches of the links have changed.
The main deterioration of a roller chain is on the rollers and roller axles of the chain links that directly receive the force applied by the sprockets that guide and urge the chain through its oven. The deterioration of the rollers and roller axles of a chain changes the length or “pitch” of the chain link. The changes of the lengths of the links of a roller chain tend to cause the overall length of the roller chain to increase. The increase of the length of a roller chain is an indication of wear of the parts of the chain. When the chain deteriorates it loses some of its strength and might break.
The replacement of oven chains usually requires several days to a week of oven downtime. Therefore, maintenance of oven chains is one of the highest priorities of a bakery maintenance department, and it is important to inspect the chain to estimate the remaining life of the chain.
When chains are to be inspected, usually the maintenance department of a bakery will stop the movements of a chain, allow the chain to cool, and remove a link of the chain and inspect it to view the wear on the link. Typically the maintenance personnel will measure the lengths of sections of chain links that is a multiple of the chain pitch. The chain must be tensioned for the inspection and multiple pitches are measured and compared to the desired lengths of multiple pitches. If the length of the chain has increased from the previous measurements, the maintenance personnel will estimate the rate of deterioration and estimate the remaining life of the oven chain. This is not a highly reliable or accurate method, but it is a process for determining wear on the chain links. This procedure usually is done in a confined space of the oven and is difficult to perform and is subject to human error. The measurements of the chain should be performed at the same temperature in order to avoid inaccurate measurements due to expansion or contraction of the chain due to different chain temperatures. The most notable change in a chain would be to observe movements between adjacent links of the chain.
For almost one hundred years calculating wear on oven chains has been a problem. Up until now there has been no expedient way to accurately and reliably measure and track chain wear in a bakery oven. As a result, oven chains usually are replaced long after they should have been, leaving the bakery a victim of reliability.
Accordingly, it would be desirable to monitor and measure the chains of high temperature ovens, such as bakers' ovens, without having to remove the chains from their operating conditions and while the chains are at any temperature, including the high operating temperature at which the oven usually operates, and to calculate the wear experienced by the chain and to determine the remaining useful life of the chain.